Question about 2001 Jeep Grand Cherokee

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Cold Radiator after replacing the thermostat Jeep 2001

Hello I have a 2001 Jeep Grand Char..I had hot air comming out of the vents and then it went cold..I had a friend that said that it was the thermostat. I replaced it then I started the jeep and it heated up but the computer said to check coolent. I check the overflow and it was full then I check the radiator and it was stone COLD? THEN I check the top hose and it was hot and the bottom hose is cold? is it a water pump or the radiator? or something elese

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  • mtclimbing Dec 25, 2008

    The radiator was cold with the old thermostat before I replaced it.

  • mtclimbing Dec 25, 2008

    Are you saying that I should drain the radiator?

  • mtclimbing Dec 25, 2008

    When I replaced the thermostat..the radiator was completly full..just cold not circulating?

  • mtclimbing Dec 26, 2008

    The temp gage on the inside dosn't get above 185 Degres or more that 1/2 way..it dosn't even come close to reaching 200 degrees

  • mtclimbing Dec 26, 2008

    The coolent is dark green NO rust..I am just very frustrated. When I take the thermostat out do I mount it back in place or do I leave it undone?

  • mtclimbing Dec 26, 2008

    The coolent is dark green NO rust..I am just very frustrated. When I take the thermostat out do I mount it back in place or do I leave it undone?

  • mtclimbing Dec 26, 2008

    In my previous comment..I have NO pressure under ther radiator cap..the cap is cold.

  • mtclimbing Dec 26, 2008

    The thermostat was replaced and a new water pump was put in today..now the check engine light is on and the machtanic won't go good for it. He said that it was on..when it wasn't This all happened when he replaced the thermostat today..could the sensor on the thermostat housing be gone? banners_signs@verizon.net

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Well there is one other thing that's a biggy.
The heater core sometimes heater cores can screw up and the circulation stop which is what is sounds like.
Not sure how the heatercore could get blocked but it is definatly having a problem
If you are feeling somthing on the bottom but not on the top it means somewhere it's not circulating.
If worse comes to worse what I would do is remove the thermostat and keep it out since it's winter anyhow and see if it starts to circulate.
When you puchase a thermostat it comes in different temps and you might have somthing for a higher temp when you purchased it.
However removing the thermostat shouldn't do any damage as far as removing it for an hr or so and check the hoses and see if the same issue is there.
If it in fact is then it's definatly the heatercore which is where the hoses in the rear go into and out of they are about 1 inch thick.
Hope this works for you either way

Posted on Dec 26, 2008

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I was a Jeep Technician (14 years) before I moved to Toyota. In my opinion, you have a defective thermostat. Jeeps normally set their normal operating temps close to 195-198 degrees. That is why the second cooling fan is present by the radiator. Not only does it come on with the AC, but it will come on when the temps reach over 205 degrees. Now, you have stated that the temps are 185 degrees. that is just way too low, and indicates a thermostat that is sticking open. The best way to check this is get the temp up to 185 degrees, and then shut it off, drain the coolant and extract the thermostat. if it is open at all, it is NO GOOD. It should he closed TIGHT. I would like to help you further, but, I need you to know the following: ...If you click on the "RATING" button, our conversations will terminate. FixYa supposedly allows you to see one solution at a time.
Rating my assistance will get you another attempt at a solution, from another expert..

Posted on Dec 26, 2008

  • Toyota Ed Dec 27, 2008

    It would be nice to know what the actual code is, the reason for the light coming on. It just be a water temperature code, "too cool, too long"...this would prevent the oxygen sensors from controlling the air-fuel mixture.

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Neither in my opinion, Are you sure your put your thermostat in the right direction? Also are you sure you have it completely full of water? Many engines have to be burped, to remove the air in the system. Have you had your radiator cap off and run the car? you should see circulation after the car is up to temperature. Please check these things!

Posted on Dec 26, 2008

  • David Johnson
    David Johnson Dec 26, 2008

    I have had the lower hose collapse. and stop circulation also.

  • David Johnson
    David Johnson Dec 26, 2008

    Going back and reading, I noticed you said the computer said to check coolant? If that is the case either your coolant sensor in your radiator is bad or you have low coolant.

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I think your water pump is going bad...you should have better circulation and both hoses should be warm or hot to the touch

Posted on Dec 26, 2008

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  • Ronnie Houston Dec 26, 2008

    you have to put in a new thermostat if you dont you wont have any heat at all

  • Ronnie Houston Dec 26, 2008

    your water pump is not working as it should you need a new one

  • Ronnie Houston Dec 26, 2008

    most check engine lights are triggered by simple things and there isnt a sensor to change on the thermostat housing. give it a few days and the light may go off on its own.youll have to be patient with the car and let it do what it needs to to adjust to having the new thermostat in it.do you have heat in the car now? i hope so

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Have you checked your heater control valve? Look under your hood find the heater hoses and track them back to a black valve. Check the valve it may not be opening to allow hot water to flow to the heater core.

Posted on Dec 26, 2008

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  • John Weathers
    John Weathers Dec 26, 2008

    If you are concerned with an air pocket issue there is a company called UView that makes a tool called an Air Lift. It pulls a 24 inch vacuum on the cooling system and refills it minus air pockets. It works great.

  • John Weathers
    John Weathers Dec 26, 2008

    After reading all of these comments I'd be willing to bet you have an air pocket trapped in your cooling system and a bad heater control valve.
    If the engine was not running hot before all this happened and the only problem you had was a loss of hot heater air then you needed a heater control valve and you got air trapped in the system when replacing the thermostat. 
    Try this, take the Jeep and drive it up an incline, so that the front is raised up, the steeper the incline the better, as long as it's safe. Now, have a bottle of coolant ready, and open the hood. When you do this, you will want the engine to have been running for no more than 10 minutes, because as you know, the radiator cap will be under some pressure. Open the cap and let off any pressure, with the engine running. Once the pressure is released, remove the cap fully. Some coolant may overflow out the cap, which is fine. Next, turn the heat on as high as it will go. Watch the radiator filler neck. If the coolant goes down, add coolant until you can't add anymore, and replace the cap. This procedure is called bleeding, and is a very common cure for Jeeps that just had work done to the cooling system.

  • John Weathers
    John Weathers Dec 26, 2008

    If you want to you can go ahead and pull the thermostat housing off again and check to be sure you have the thermostat installed correctly. I believe you do since you sound pretty knowledgable. 
    I my 35 years fixing cars everytime I have seen someone install a thermostat backwards the engine ran hot fast even at an idle. I wish you luck with your problem I wish it was here in my shop because I'd have it fixed in 30 minutes. Hope I was helpful. Let me know if you need anymore help.

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It can be heater core has a cavity with air (radiator flush will help). Also you can replace the radiator cap. An old one that is worn out will cause the hot air to escape therefore not blow hot air.
Sometimes when you are new at self repair a comon mistake when replacing a thermostat can be putting it in upside down the will cause your heater to blow cold air as well.
So check for these three issues. If it bad water pump car would be overheated.
Good Luck

Posted on Dec 26, 2008

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Check your heater core it is most likely the problem

Posted on Dec 26, 2008

  • machadojr_fe Dec 26, 2008

    make sure that there are no pressure leaks in the coolant system

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Engines return hot coolant to the radiator through top hose, and cooled coolant goes back to the engine through the bottom hose, so a difference in temperature between the two would not be unusual.
Assuming you have allowed the engine to come up to temperature and the bottom hose is stone cold, either the radiator or bottom hose is blocked, the water pump has failed or there is an air lock. A seized viscous coupling on a cooling fan or a permanently running electric fan can also make the radiator over-cool, but the bottom hose would feel slightly cooler than the top hose, not cold. 
The thermostat is on the return side of the coolant loop. IE it is at the engine end of the lower hose. What is your thermostat reading in the dash? If it's climbing above halfway then you probably have a faulty thermostat. I presume that the system is completely full etc.
you may need to bleed the air out of the system try pulling the heater pipe off the right side of the engine
In my opinion it should be normal with a low temperature at the lower hose. The water comes from the engine in the top hose to the radiator when warm enough, if cold it goes via the thermostat back to the waterpump. The radiator use the wind due to speed or the electric-fan or both to make the water cold again. The outlet from the radiator is the lower hose and that goes to the waterpump. 
The temp gauge inside the car should be around the middle of is range. I have noticed that my gauge shows a little bit lower after the change of radiator. It must be because it is very clean and all the metallparts in it is there. It has bigger cooling area in other words.
It is difficult to judge how hot or cold anything is when reading another persons measurment using his/hers hands. Normally one person can hold things up to 50-60 degrees C. Above that it is too warm for most people. The thermostat is opening around 80 something degrees. That means that I don't think your car was warm enough to let the radiator work properly.

Try flushing the coolant sys.   I would pull the radiator and flush it by its shelf.  I know that the track/kicks have the inlet and the outlet on the same side so put the radiator on its side with the in and out towards the top and see how much water it holds.  Then flush the block.  If there is rest or debree in the sys you dont want to run it into the radiator. 

Posted on Dec 25, 2008

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It could also be whats called airlock, when you filled the radiator did it take a long timke to fillit up,had a simular situation with my silverado pickup.

Posted on Dec 25, 2008

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It could be your serpentine belt, thermostat or water pump.
to open the radiotor drain--------
'Facing your Grand Cherokee Laredo, the pitcock is on the bottom right of the radiator. You should be able to reach around the bottom valance (with the engine cool) and feel the pitcock. It is a small plastic valve and should have a 8\" tube (which is too short in my opinion) attached. The valve should turn 3/4 of a turn. If it only turns 1/4 turn you may have to apply slight force.

==============
The HeaterTreater is an after market kit that solves heater and AC for the Jeep Grand cherokee and Laredo. It is much cheaper than the dealership fix and is easy to install. For diagnosis and info, check out www.heatertreater.net or search ebay for "heatertreater".

Posted on Dec 25, 2008

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Hi and welcome to FixYa,

Initially, re-check/replace the new thermostat. Possibilities are:

  • the new is a dud;
  • stuck on close;
  • installed the other way around.
You could try testing a thermostat. On room temperature, it should be close. Put it in boiling water and it would open.

Good luck and Thank you for using FixYa. Happy Holidays.

Posted on Dec 25, 2008

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  • Louie  Role
    Louie Role Dec 25, 2008

    Pls refer to below image

    Alternate possibility is airlockinside the water galleries of the engine. A temporary workarouond is to drill a hole in the thermostat to assist with air bleeding out of the block in case the thermostat is not opening (air locked).

  • Louie  Role
    Louie Role Dec 25, 2008

    Have you tried checking the thermostat with boiling water?
    Alternately, you can checking coolant flow to the radiator without a thermostat installed (at least temporarily).


  • Louie  Role
    Louie Role Dec 26, 2008

    The radiator/cap is cold/no pressure, but the engine has warmed up. The hot coolant from the engine in not flowing to the top of the radiator to displace the cold coolant. Either the water pump is not working (unlikely), the thermostat is closed or is it not allowing the coolant flow. Try to replace or even just remove the thermostat and run the engine again.

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  • 327 Answers

It is water pump that is having the problem.

Posted on Dec 25, 2008

  • classyexpert Dec 25, 2008

    yes.as per the otherexperts solution try draining the radiator.
    radiator drain **** located

    It is near the bottom left side of the radiator as you face the front of the Jeep. You have to remove the Headlight and grille to be able to access it, sounds like a pain but it takes about 5 min to do. It is a 'twist fit' stopper so be careful when attempting to open it. 

    to drain the Radiator on a Jeep Grand Cherokee

    Should be a plug either at the bottom or rear of radiator 

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I would recommend u remove the thermostat and see if u have flow, you will be able to see coolant movement by looking in the radiator as soon as u start the engine, if u see no flow then it is possible the impeller on the water pump has come loose, this happens but it is no something u see everyday, also u never said was the old coolant rusty? if it was there could be a clog at the bottom or top of the radiator and it would stop flow, the best way to check this is to pull the radiator out and back flow it (pump water in the lower hose connector) and see if water gushes out, use a high pressure garden hose, let me know the results of these tests if u don't find the problem, but I think u will if u follow my inspection procedures.

Posted on Dec 26, 2008

  • yadayada
    yadayada Dec 26, 2008

    I wanted to add that I have been doing this work for 30 years and have seen every kind of cooling system issue, including yours, most times it is the thermostat is backwards or defective, the rest are radiator and water pump problems.

  • yadayada
    yadayada Dec 26, 2008

    Lets see, u can't have time to do what I suggested (or any else for that matter), Why even ask for assistance if u don't do as suggested it is sound advice, by reading your replies i surmized u have no mechanical expertise in this area of car repair, just request your money back and take it to a pro who will just do the things I suggested (and other experts) and charge u $100's. do u think there is a magic wand to fix this problem? no just hard work and the process of elimination just as we do at the shops many of us work for, I have over 30 years as a professional auto technician, I am a ASE master technician and a Ford factory certified Master technician, I gave u sound advive, just follow it and your frustration will be rewarded with a fixed problem.

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